1. Field of the Invention
The present invention relates to a marine vessel which includes a propulsive force generating unit having an engine with an electric throttle as a drive source, and a marine vessel running controlling apparatus for such a marine vessel.
2. Description of the Related Art
An exemplary propulsion system provided in a marine vessel such as a cruiser or a boat for a leisure purpose is an outboard motor attached to a stern (transom) of the marine vessel. The outboard motor includes a propulsion unit provided outboard and including an engine as a drive source and a propeller as a propulsive force generating member, and a steering mechanism which horizontally turns the entire propulsion unit with respect to a hull of the marine vessel.
A control console for controlling the marine vessel is provided on the hull. The control console includes, for example, a steering operational section for performing a steering operation, and a throttle operational section for controlling the output of the outboard motor. The throttle operational section includes, for example, a throttle lever (remote control lever) to be operated forward and reverse by an operator of the marine vessel. The throttle lever is mechanically connected to a throttle of the engine of the outboard motor via a wire. Therefore, the output of the engine is controlled by operating the throttle lever. A relationship between the operation amount (operation position) of the throttle lever and the throttle opening degree is constant.
In a typical engine, a relationship between an engine speed and the throttle opening degree is nonlinear. In a lower throttle opening degree range of the typical engine, as shown in FIG. 29, the engine speed steeply increases with an increase in the throttle opening degree. In a higher throttle opening degree range of the engine, the engine speed moderately increases with the increase in the throttle opening degree. This tendency is particularly remarkable in the case of a throttle including a butterfly valve. A throttle employing ISC (idle speed control) also exhibits this tendency to some degree.
Particularly, such a nonlinear characteristic significantly influences the control of a small-scale marine vessel including an outboard motor having no speed change gear. More specifically, as shown in FIG. 30, a resistance received by the marine vessel from a water surface is relatively small in a lower speed range, and varies in a complicated manner due to a frictional resistance and a wave-making resistance. In addition, the engine speed is steeply changed in response to a slight throttle operation, so that a propulsive force generated by the outboard motor is liable to be changed. When fine control of the propulsive force is required, for example, when the marine vessel is moved toward or away from a docking site or moved to different fishing points, a higher level of marine vessel maneuvering skill is required. Therefore, an unskilled operator of a leisure boat or the like cannot easily control the throttle lever when moving the boat toward or away from a docking site.
On the other hand, the engine is required to have higher responsiveness in a middle-to-high speed range which is higher than a hump range (corresponding to an engine speed of about 2000 rpm at which a maximum wave-making resistance is observed). This is because the marine vessel is preferably quickly brought into a smooth traveling state (planing state) out of the hump range and has higher responsiveness for traveling over surges. Therefore, the engine speed is required to be quickly changed in response to the operation of the throttle lever in the middle-to-high engine speed range. However, the throttle opening degree-engine speed characteristic shown in FIG. 29 does not meet this requirement.
In the automotive field, electric throttles have recently been used, which are driven by an actuator according an accelerator operation amount detected by a potentiometer. It is conceivable to use such an electric throttle for the engine output control of the propulsion system such as the outboard motor. In this case, the throttle lever operation amount-throttle opening degree characteristic, which is defined as a fixed linear relationship in the prior art arrangement having the throttle lever and the throttle mechanically connected to each other, can be flexibly modified. For example, the operation amount-throttle opening degree characteristic can be nonlinear. Therefore, the marine vessel maneuvering characteristic for lower speed traveling (with a lower throttle opening degree) can be improved by properly setting the operation amount-throttle opening degree characteristic.